1. Field of the Invention
The present invention relates generally to conveyors for aggregate material and, more particularly but without limitation, to conveyors for conveying hot mix asphalt material in an asphalt paving machine.
2. Description of the Related Art
Hot mix asphalt material used in highway construction and the like ideally consists of a uniform mixture of several sizes of mineral aggregate and liquid bituminous asphalt cement. When properly blended in the correct proportions, the hot mix asphalt material provides a uniform and durable material that is capable of withstanding heavy traffic and loads over a long service life. In the process of producing the hot mix asphalt material and delivering it to a construction site for placement by an asphalt paver, however, the mixture may tend to separate into its constituent parts, a condition commonly referred to in the industry as xe2x80x9csegregationxe2x80x9d.
For instance, the hot mix asphalt material produced at the production plant is often loaded into a storage silo to await trucks for transport to the construction site. As the hot mix asphalt material is carried by a conveyor to the top of the silo, the larger sized aggregate contained in the hot mix asphalt material tends to separate from the smaller sized aggregate material contained therein. Further, as the hot mix asphalt material is dropped from the conveyor into the silo, the larger sized aggregate tends to roll to the lower periphery of the pile of hot mix asphalt material typically forming a pyramid near the center of the silo, while the smaller sized aggregate tends to cling to the top and sides of the pile. The hot mix asphalt material within the silo is, therefore, no longer a uniform mixture as desired but, instead, is a segregated mixture consisting of a surplus of larger sized aggregate near the outer wall of the silo and a paucity of larger sized aggregate nearer the center of the silo.
Similarly, as the hot mix asphalt material is discharged from the silo into trucks for transport, larger sized aggregate tends to roll to the extreme corners of the truck box while the smaller sized aggregate tends to remain more toward the center of the truck box. The truck therefore contains a segregated mixture consisting of a surplus of larger sized aggregate at the front, rear and sides of the truck box and a paucity of larger sized aggregate nearer the center of the truck box.
An asphalt paver at the construction site is generally a state-of-the-art self-propelled construction machine designed to receive, convey, distribute, profile and partially compact the hot mix asphalt material. The paver accepts the hot mix asphalt material into a receiving hopper at the front of the machine, conveys the material from the hopper to the rear of the machine with parallel slat conveyors, distributes the hot mix asphalt material along the width of an intended ribbon or mat by means of two opposing screw or spreading conveyors, and profiles and compacts the hot mix asphalt material into a mat with a free-floating screed.
Each slat conveyor that moves the hot mix asphalt material from the receiving hopper to the rear of the paving machine generally consists of two parallel slat chains with a multitude of transverse slats connected there between. Each slat chain is pulled by one of two sprockets mounted on a common shaft which, in turn, is driven by appropriate power transmission chains, gear boxes or the like. Because the slat conveyor pulls the hot mix asphalt material from the hopper in a bulk mass with little or no remixing, any segregated characteristics of the hot mix asphalt material as it exists in the hopper continues to exist in the hot mix asphalt material as it is placed by the opposing screw conveyors on the subgrade in front of the screed.
Thus, when the undesirably segregated, hot mix asphalt material is delivered to the construction site and placed by the asphalt paver, the mat produced is not of uniform consistency but, instead, contains regions having a surplus of larger sized aggregate and a paucity of smaller sized aggregate and, likewise, regions with a surplus of smaller sized aggregate and a paucity of larger sized aggregate. As a result, the mat produced from the segregated material does not possess the desired mechanical properties and generally will not withstand the anticipated loads and stresses as well as a mat constructed of non-segregated, or uniform, hot mix asphalt material.
What is needed is an apparatus that is capable of, and a method for, remixing segregated hot mix asphalt material just before the hot mix asphalt material is placed on a subgrade by an asphalt paver whereby the detrimental effects of segregation are substantially or totally eliminated.
An improved asphalt paver having a remixing conveyor system is provided for substantially or entirely eliminating segregation in hot mix asphalt material delivered to the asphalt paver. The remixing conveying system includes at least one pair of parallelly spaced, oppositely pitched, counter-rotating feed augers, each auger of which has remixing blades that intermittently displace portions of the hot mix asphalt material generally transversely to the direction that the feed augers convey the hot mix asphalt material from a hopper of the asphalt paver to spreading augers that are used to laterally distribute the hot mix asphalt material near the rear of the machine. In order to regulate the rate at which hot mix asphalt material is placed by the asphalt paver, the feed augers are driven by speed-controllable hydraulic motors.
A plurality of elongate members, one above each of the feed augers, are adapted to provide protection for the respective feed augers from impact forces generated as hot mix asphalt material is dumped into the hopper, to prevent overloading of the feed augers that might otherwise arise from excessive hot mix asphalt material being heaped on the feed augers, and to promote enhanced lateral extraction of the hot mix asphalt material from the hopper by the feed augers. A feed screen, having a mesh-like structure constructed of bar or rod material and generally supported by the elongate members, may be optionally used to further enhance the extent of lateral extraction of the hot mix asphalt material from the hopper by the feed augers.
The present invention also provides a kit for replacing each conventional slat conveyor of an existing asphalt paving machine with two parallel, oppositely pitched, counter-rotating feed augers that serve the purpose of the slat conveyors in moving hot mix asphalt material through the paver from the hopper to the spreading augers, but also serve the purpose of remixing the hot mix asphalt material into a uniform consistency and thereby provide desegregating capability in an existing paving machine.
The present invention also provides a method for substantially or entirely eliminating segregation in hot mix asphalt material delivered to an asphalt paver. The method includes displacing the hot mix asphalt materials intermittently generally transversely as the hot mix asphalt material is conveyed by at least one pair of parallel, oppositely pitched, counter-rotating feed augers from a hopper to spreading augers of the asphalt paver.
The principal objects and advantages of the present invention include: to provide an asphalt paver that eliminates segregation in hot mix asphalt material delivered to the asphalt paver; to provide such an asphalt paver that includes at least one pair of parallel, oppositely pitched, counter-rotating feed augers for conveying hot mix asphalt material from a hopper of the asphalt paver to spreading augers of the asphalt paver; to provide such an asphalt paver that includes feed augers having paddle mechanisms that intermittently and generally transversely displace hot mix asphalt material being conveyed by the feed augers; to provide such an asphalt paver having feed augers with controllable rotational speeds; to provide such an asphalt paver having feed augers that are driven by hydraulic motors; to provide such an asphalt paver that has elongate members superimposed over feed augers for protecting the feed augers, for preventing overloading of the feed augers, and for enhancing lateral extraction of hot mix asphalt material from a hopper of the asphalt paver by the feed augers; to provide such an asphalt paver having a feed screen for controlling the flow of hot mix asphalt material to feed augers of the asphalt paver; to provide a kit for converting existing asphalt pavers whereby those pavers can substantially or entirely eliminate segregation in the hot mix asphalt material delivered to those pavers; to provide a method that is consistent with any or all embodiments of such an asphalt paver having a remixing conveyor system and with a kit for converting existing asphalt paving machines as herein provided; and to generally provide such an asphalt paver, kit and method that is economical to manufacture, efficient in operation, reliable in performance, capable of long operating life and/or particularly well adapted for the proposed usage thereof.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.